mIRC can act as an identd server and will send the specified User ID and System as identification. This server will be more useful to some people than others. In general it is better to leave it active as some systems might refuse a connection if there is no reply to an identd request.
Enable Identd Server
Check/uncheck this to turn the identd server on or off
This can be your account or user name on your system. For most people this will be the User ID portion of their email address (the text before the @ sign). Valid characters for a User ID are: . 0-9 A-Z _ - a-z
This identifies your operating system. For all intents and purposes, replying with a value other than UNIX would not be very useful for most people.
This should usually be 113.
Show Identd requests
This displays any identd requests sent to your identd server if it is turned on.
Enable only when connecting
This turns the identd server on only when you are connecting to an IRC server. The moment an identd request is received and replied to, or the moment you connect to the IRC server and see the MOTD, the identd server is turned off.
Note: This server will reply to all identd queries sent to the specified port ie. it is not limited to replying to an IRC server for mIRC. If you have turned on the identd server and it is not replying to identd queries then it is probable that the type of internet account you have is preventing mIRC from replying, or that another program is running which has control of the identd port.
Use ID from email address
Makes mIRC use the User ID from your email address in identd replies.
You can also use the /identd [on|off] [userid] command to change the above settings.